It has been known for some time that over-exposure of the skin to UV radiation can result in damage to the skin which varies in severity from slight reddening and accompanying soreness to severe burning. Further, over-exposure to UV radiation, especially to the shorter wavelengths of UV radiation, namely 280 nanometers to 320 nanometers, it is believed can lead to the development of skin cancer, especially melanoma. The risk of one developing skin cancer or other complications depends on the quantity of UV radiation to which the skin is subjected. It has also been found that people whose skin pigmentation is relatively light in colour, in other words, fair-skinned people, tend to have less tolerance to UV radiation than those of darker skin
The skin reacts to radiation by changes in the melanin content. However, prior to a change in the melamine content, reddening occurs and then subsequently soreness and burning ensue. To facilitate quantifying the minimum dose of UV radiation an individual can tolerate, the dose of UV radiation which induces reddening in the skin is referred to as the Minimum Erythemal Dose, hereinafter referred to as MED. A fair-skinned person, in general, can tolerate approximately one MED, while a rugged skinned person with well tanned skin who rarely burns could tolerate up to twelve MED3 s or more. An individual would normally be subjected to one MED of UV radiation in equatorial regions at midday in approximately ten to fifteen minutes.
It is believed that the active component of the UV radiation is the UVB element of the spectrum. Specifically, the element of the spectrum of wavelength of the order of 280 nanometers to 320 nanometers.
Devices for monitoring the quantity of UV radiation received by the skin, in general, are referred to as sun dosimeters. Usually, dosimeters comprise a support member and a photochromic material which is sensitive to UV light of wavelength in the range of 280 to 320 nanometers. A plurality of reference colours or shades are provided round the photochromic material. The reference colours correspond to the colour or shade the photochromic material would achieve after being subjected to respective specific doses of UV radiation. These devices, in general, are placed adjacent or on a sunbather, and exposed to the sun while the individual's skin is similarly exposed. Periodically, the individual can check the colour or shade of the photochromic material against the reference colour to establish the dose of UV radiation to which the device and skin have been exposed. However, while these devices are adequate for an individual sunbathing for a single uninterrupted period per day, they are inaccurate for use where the individual sunbathes for a number of periods each day. The reason for this is that the photochromic materials are reversible materials. In other words, when the photochromic material is no longer exposed to UV radiation, the material begins to revert to its original colour or shade. Depending on the photochromic material used, this reversal procedure may be fast or slow. Clearly, the faster the reversal procedure, the less effective these devices are, since the effect on the skin of UV radiation is cumulative over a day. Accordingly, where an individual takes a number of breaks from sunbathing during a day and the dosimeter is unexposed to the sun during the periods of the breaks, the dosimeter commences to reverse o being removed from the UV radiation
There is therefore a need for a method and device for monitoring the quantity of UV radiation to which an individual's skin is subjected which overcomes the problems of known methods and devices.